The Contractor shall exert its best efforts to study various strains of mice for responsiveness or unresponsiveness to H-2 D.2 antigen. Congenic resistant strains, including a congenic B10.A responder strain now being developed, shall be used to identify H-1 linked and nonH-2 linked genes. To find the site of gene action, humoral and cellular responses of responder and non-responder mice shall be compared, using the antibody-complement-mediated cytotoxicity and hemagglutination assays to test for antibodies and the MLC and LMC to check for cell-mediated immunity. Immunologic and genetic studies shall be carried out to determine the basis for the observation that mice of certain strains do not make antibodies against histocompatibility antigens when immunized with H-2 non-identical normal mouse tissue, whereas they do make antibodies to these antigens when immunized with leukemic cells.